This NYC-based project will evaluate the performance (sensitivity and specificity), cost-effectiveness, and feasibility of using a new fourth generation HIV test which detects both IgM antibody and HIV p24 antigen. Populations of persons attending a pair of sexually transmitted disease clinics, two bath houses catering to men who have sex with men (MSM), and a busy urban hospital Emergency Department will be offered screening with three different HIV test types (rapid point of care test, pooled nucleic acid amplification testing, and fourth generation test), and a longitudinal study of men attending bathhouses will be conducted to evaluate repeat testing as an AHI detection strategy in high risk MSM. Targeted hepatitis C screening and universal hepatitis B Screening will be done in the STD and MSM populations to examine the feasibility of operationalizing new, expanded guidelines for hepatitis B screening and public health management. Traditional (provider referral) and internet partner notification approaches will be evaluated; phylogenetic analysis of HIV will be done to measure the degree of relatedness between HIV from different case-patients and partners. Phylogenetic and antiviral resistance patterns will be used to inform and elucidate the sexual networks described by traditional partner notification activities. PUBLIC HEALTH RELEVANCE: Acute HIV infection (AHI) is a serious public health concern because HIV is highly transmissible during the acute phase of infection and infected persons are often unaware of their infection and at risk to transmit to others. The potential public health advantages of the NYC STOP project are: 1) identification of AHI cases, 2) prevention of secondary transmissions through counseling of AHI patients and thorough partner notification processes, and 3) gaining knowledge about the performance of a candidate HIV screening test which could expand the availability of AHI screening. Early diagnosis and notification can improve health outcomes by facilitating early referral to treatment.